1. Field of the Invention
This invention relates generally to apparatus and methods for shutting off flow in a conduit, and more particularly to an apparatus and method that requires only minimal excavation to expose the top surface of a buried pipe main and utilizes an anchor apparatus installed in the excavation to support an elongate hollow tube normal to the main in sealing relation on the exterior of the main through which tools are passed to form a hole in the side wall of the main, removably install inflatable bladders to seal off the flow in the main while repairs are made downstream, and to plug the formed hole when repairs are completed.
2. Brief Description of the Prior Art
One of the many important tasks for a gas utility is to respond to emergencies that involve or may involve natural gas. The types of emergencies vary, but one of the more important, involves a broken or breached gas main. Gas mains can be damaged in many ways, such as breakage from excavating equipment (i.e., backhoe), excessive soil settlement, failure due to age, and washouts from broken water mains. When a gas main is breached or broken, the gas normally transported and contained within the pipe escapes to the atmosphere causing a fire or explosion hazard. If the failure is due to a washout, water can enter the main, flood the gas system, and cause a loss of service to the attached customers. In either case, the gas utility must regain control as quickly as possible by stopping the escaping gas or influx of water. Conventional methods for blocking flow in buried gas mains require extensive excavation to completely uncover the main for deployment of plugging equipment and are quite time consuming.
One common method for blocking flow in the main is to attach a saddle to the main and install equipment to drill into the main and insert a stopper. Typically, the saddle mounting hardware consists of bolts or chains that attach to each side of the saddle and wrap around the pipe. Some mechanical method of tightening the bolts or chains is usually supplied. To install the saddle clamping chains or hardware, soil must be excavated completely around the pipe to allow access from all sides so that the chains or hardware can be wrapped under the main, and the exterior of the pipe must be extensively cleaned to allow sealing. As a result, excavations are large and many times must be hand dug, increasing excavation time. This extra excavation and extensive cleaning adds significant amounts of time to the stopping process, thus increasing the danger from potential explosions, fire damage or the influx of water. In addition, the current drilling and stopping equipment take a long time to set up and complete the job once the main is exposed.
Calandra, U.S. Pat. No. 4,013,097 discloses an apparatus for damming the flow of fluid in a pipeline comprising an inflatable bladder attached to the end of an elongate umbilical tube and encompassed within a flexible outer bag of resilient material with a viscous fluid between the bladder and the bag. The apparatus is deployed parallel to the longitudinal axis of the pipeline and the bladder is inflated to force, through the viscous fluid, the outer bag into sealing engagement with the pipeline interior.
DeGiovanni, U.S. Pat. No. 4,155,373 discloses a method for shutting off gas flow in plastic pipes wherein a tubular plastic fitting is joined to the wall of a plastic gas pipe by fusion and a hole is cut through the plastic gas pipe and then a balloon-type stopper is inserted into the gas pipe and inflated.
Yie et al, U.S. Pat. No. 4,291,727 discloses an inflatable expandable flexible sleeve and insertion apparatus which is connected to a saddle attached to the pipeline by U-bolts. To install the saddle clamping U-bolts, soil must be excavated completely around the pipeline.
Minotti, U.S. Pat. No. 4,351,349 discloses pipe repair kit including an inflatable bladder and a system of conduits which are secured to the pipe exterior in longitudinally spaced relation by a plurality of two-piece clamps which extend completely around the circumference of the pipe. This method and apparatus requires a large excavation and the soil must be excavated completely around the pipeline at several locations.
The present invention is distinguished over the prior art in general, and these patents in particular by an apparatus and method for shutting off fluid flow in a pipe main while repairs are being made which requires only exposure of the top surface of a buried main and only minimal cleaning of the exposed surface. An anchor system installed in or above the excavation supports an elongate tubular seal tube against the exposed surface of the main to extend radially therefrom. A jack mechanism compresses the lower end of the seal tube containing a seal member against the exterior surface of the main. A tubular cutting tool installed inside the seal tube is rotated by an air motor to cut a hole in the side wall of the main. A tubular sealant application tool installed inside the seal tube has a nozzle at its bottom end that sprays liquid sealant material onto the interior surface of the main and is then removed. A tubular bladder deployment tool installed inside the seal tube carries a pair of deflated bladders. The bladders are deployed from the deployment tool in opposed direction into the interior of the main along the longitudinal axis of the main and are then inflated to expand and form a seal to shut off fluid flow in the main. After repairs have been made, the bladders are deflated and retracted and the bladder deployment tool is removed. A tubular thread tapping and plugging tool is installed inside the seal tube and rotated to form threads in the cut hole and then removed and then installed again to secure a threaded plug into the hole. After the hole has been plugged, the seal tube is removed.